Tyvek

DuPont Tyvek is made of high-density polyethylene (HDPE). It is not paper, but can be recycled for use in a variety of new products, including plastic lumber for picnic tables, park benches, construction fencing and also mud flaps.
To recycle small quantities (less than 25 envelopes per month), turn any Tyvek envelope inside out, so the unprinted white surface shows on the outside. Stuff the inside-out Tyvek envelope with other used Tyvek envelopes for recycling. Address and mail the envelope to: Tyvek Recycling Specialist, CRP-Bldg. 705, 974 Centre Road, Wilmington, DE, 19805-0705.